Meeting Abstract
Colonization of new environments exposes organisms to novel combinations of abiotic factors that have the potential to drive adaptive divergence, although studies investigating the interactive effects of multiple abiotic factors on the evolution of physiological traits remain rare. Here we examine the effects of low salinity, low temperature, and the interaction between these factors on the growth of three North American populations of the threespine stickleback fish (Gasterosteus aculeatus) representative of the putative ancestral marine and anadromous ecotypes and the derived freshwater ecotype. In north-temperate freshwater habitats, stickleback experience a combination of low salinity and low winter temperatures that are not experienced by the ancestral marine and anadromous forms. Here we show that both salinity and temperature and the interaction between them have stronger negative effects on the marine and anadromous populations compared to the freshwater population. Freshwater stickleback showed only a small (~10%) reduction in specific growth rate (SGR) for mass when exposed to 4°C, while marine and anadromous stickleback showed sharp declines in SGR (82% and 74% respectively) under these same conditions. The modest decreases in growth rate in freshwater stickleback with exposure to low winter temperatures in fresh water strongly suggest that this population has the capacity for physiological compensation to offset the negative thermodynamic effects of low temperature on growth, which is consistent with adaptive evolution in response to the interactive effects of low salinity and low temperature during freshwater colonization.
